In today's communications, digital networks transport large amounts of information. Network services can be, for example, traditional voice phone, facsimile, television, audio and video broadcast, and data transfer.
With the increasing need of information exchange in the global society, the capacity of existing and future networks must be used efficiently. Multiplexers switch different network services to a single network in such a way that every service is fully maintained and does not disturb other services.
Asynchronous Transfer Mode (ATM) is one of the most commonly used communication protocols. ATM is a connection-oriented protocol. ATM protocol assigns virtual channels to each ATM cell. The virtual channel is supported by a physical link. ATM protocol compliant devices process information by framing the information to ATM cells. An ATM cell includes a payload as well as a header. The header includes various fields that map the ATM cell to the virtual channel. These fields include the virtual channel identifier (VCI) field and the virtual path identifier (VPI) field.
The ATM cell is associated with a physical layer (PHY) value that represents the physical link on which the ATM cell arrives or originated from. A device, such as a media access unit, an UTOPIA bus manager as well as an ATM switch associate the PHY value with the ATM cell.
Various adaptation layers were developed in order to enable ATM based network to support a variety of services and protocols that are not based upon ATM technology, such as IP, Gigabit Ethernet, Frame Relay, SONET, SDH and wireless application. Five types of adaptation layers were defined AAL1-AAL5. Each adaptation type layer supports different services. AAL5 is very popular. It adapts multi-cell higher layer payloads (or frames) into ATM with minimal error checking and no error detection. AAL5 assumes that the conveyed data is sequential from the end user and uses the Payload Type Indicator (PTI) bit to indicate the last cell in a transmission
Multiple ATM cells can convey one upper layer frame. Various scheduling mechanisms were developed in order to schedule the transmission of ATM cells. U.S. patent application publication serial number 2004/0081167 of Hassan-Ali et al., U.S. Pat. No. 6,813,272 of An et al., U.S. Pat. No. 5,831,975 of Chen et al., U.S. Pat. No. 6,665,301 of Wu, U.S. Pat. No. 6,795,445 of Kabie et al., and U.S. Pat. No. 6,687,229 of Kataria, all being incorporated herein by reference, illustrates various devices and method for scheduling ATM traffic.
In some cases the number of possible allocated VCI values is smaller than the overall number of traffic threads originating from a serviced group of users. ATM defines a single channel for each combination of VPI/VCI, especially when using AAL5 adaptation layer. Merely assigning the same VPI/VCI values to different threads can cause undesired information interleaving.
A Digital Subscribers Line Access Multiplexer (DSLAM) may face such a problem. A DSLAM is connected between a backbone network and between many users via digital subscriber modems. A single DSLAM can be connected to many users. Each user can exchange various types of information (data, video, audio), using a single cable modem. Typically, each type of traffic can be associated with a different kind of quality of service. In many cases there are not enough VPI/VCI combinations for each traffic thread. In addition, merely providing the same quality of service to all the different types of traffic is inefficient and can cause timing violations.
There is a need to provide efficient methods and devices for scheduling ATM cells.